Brit here: agree with the last two posters, that "off Wednesday and after" is very much the usual meaning. I tend, however, to say something like "from Wednesday inclusive" -- just because of the semi-rule in life that "anything which can be misunderstood, will be misunderstood".

I agree. 'From Wednesday' would mean you wouldn't be seeing me on Wednesday, but like cabbageweevil, if it was important (say, if I'm arranging time off) I'd probably say "From Wednesday to Friday, inclusive."